Baking science: Egg whites, what’s the big deal?

Egg whites are a funny thing. They can make your cakes soft and angelic, or dry and brittle.

Unlike other ingredients in baking like baking soda, baking powder or yeast, which rely on the chemical properties of food, egg whites are affected by physical properties. Whisked egg whites works by trapping air within the liquid, creating a foam.

Let’s take a moment to appreciate this hand whisk bought in 1996. Still works fine! I love my Kitchenaid to bits but baking doesn’t have to be fancy at all.

Do’s

Wipe down your bowl with vinegar to remove traces of fat. Fat affects the formation of a stable egg white foam.

Separate the egg yolks from the whites cleanly. Egg yolks contain fat, which again affects the stability of the egg white. However, I have been lazy and stingy. I didn’t want to restart my cake batter when I accidentally popped an egg yolk in the purity of the egg white. A little bit of egg yolk won’t affect the ability of the egg white to foam up, but will affect the stability of the egg white before being set by baking. In the end, my cake was fine.

Use fresh eggs. Older eggs won’t foam up as much.

Add cream of tartar when beating the egg whites – especially when using old eggs. Adding an acid changes the pH of the egg white and helps it to foam. But adding an acid will also decrease the foam’s stability.

Don’t

Overwhip. Like with whipped cream, you will get more experienced with how it should look and feel. You may even want to switch to hand-whisking when it looks close to the stage of your desired result.

Overwhisking causes smaller air bubbles to form. This decreases the elasticity of the foam and causes it to become more unstable. Egg whites which have been whisked beyond the stiff peak stage won’t expand as much, and will become brittle – leading to drier crumbs in your cake. [More on this in the blogpost Why is my spongecake so dry?]

If hand whisking, use an up-and-down circular motion rather than flat stirring inside the bowl. This may seem obvious but necessary to explain! The aim is to incorporate air – an up-and-down motion catches and traps air so use big arm motions to own it.

Use a plastic bowl. Running your fingers inside of the bowl, you may often feel traces of oiliness from past baking. Plastic holds onto fat more easily and will cause the egg whites to reduce the volume.

Hope this debunks some myths about egg whites. Understanding how it physically changes can help you develop your own preference and saves you some kitchen experimentation.